The invention falls within the surveillance field, in particular maritime surveillance when the platform in question is a ship.
In the context of maritime surveillance, the ships supply self-declarative information providing the identification, position, route and dimensions (length and width) of the ship, according to an automated identification system (AIS).
It is useful to be able to verify this information supplied by a ship, in order to detect suspicious ships, in a civilian or military context.
To that end, it is known to use information supplied by a radar system. In a known manner, a radar system includes a transmitter able to transmit electromagnetic radio waves, and a receiver for reflected electromagnetic radio waves, and computation means making it possible to determine the power backscattered by a target based on the distance between the latter and the radar.
Such an operating mode of a radar system is known by the name “range-profile” mode. The definition of the range-profile corresponds to the depiction of the power backscattered by the detected platform as a function of the distance. The range-profile of a target can only be established when it has been detected beforehand using a detection mode.
In the state of the art, it is known to provide a signal of the “range-profile” type to an operator, on a graphic display interface, the operator then being able to move cursors on the graphic interface to perform a manual estimate of the dimension, for example the length, of the observed ship.
Indeed, based on the position of the radar system relative to the axis of the observed ship, the radar system makes it possible to detect the length or width of the ship, or more generally of the observed platform.
It is then possible for the operator to compare the computed dimension with a corresponding dimension, obtained from the AIS identifier received from the observed ship.
However, such a manual operation takes time from the operator, and can also be imprecise.
In addition, in the maritime context, radar measurements are noisy due to the environment (presence of sea clutter), and it is therefore difficult for a human operator to effectively use a noisy signal displayed on a graphic interface.
It is therefore desirable to automate the estimation of dimensions of a moving platform such as a ship, to avoid the aforementioned hazards.
More generally, in the field of remote monitoring, it is desirable to be able to estimate the dimensions of a moving platform automatically, in particular in environments where radar measurements are noisy.
To that end, according to a first aspect, the invention proposes a method for automatically computing a dimension of a moving platform, said dimension being a length dimension or a width dimension, including a step for sending, by a radar system, electromagnetic radio waves toward said platform along a predetermined transmission axis and acquiring at least one digital power profile signal representative of a received reflected signal power as a function of a radial distance along said transmission axis relative to a reference point of said radar system. The method includes the following steps:                applying a filtering operator on the acquired digital power profile signal making it possible to obtain a filtered digital signal,        determining, by computation, a first radial distance corresponding to a first variation peak of the filtered digital signal and a second radial distance corresponding to a second variation peak of the filtered digital signal,        computing a radial dimension of the platform as a function of said first and second radial distances.        
Advantageously, the method according to the invention makes it possible, owing to the application of a filtering operator, to obtain a filtered signal that makes it possible to minimize the influence of the noise and sea clutter, and to process the filtered signal automatically to obtain a dimension of the observed platform.